Firstly, the structure of scientific argument is logically based and, to engage with some of the knotty problems we address, a firm grasp of the principles of logical argument is required. Many of the controversies and internal arguments that have dogged the discipline over the years have arisen out of a failure to understand the logical basis of the discussion.

Secondly, for many of us words and the rules of argument are the tools of our trade as we engage in the business of helping people change their behaviour, thoughts and feelings, whether in a clinical, educational or business setting. It is important to understand the basis of the leverage that logic and rhetoric gives us in our work.